Alterations in adrenergic receptor signaling in heart failure

Driving force of deteriorated cellular environment in heart failure: Metabolic remodeling

Heart Failure (HF) has been one of the leading causes of death worldwide. Though its latent mechanism and therapeutic manipulation are updated and developed ceaselessly, there remain great gaps in the cognition of heart failure. High morbidity and readmission rates among HF patients are waiting to be addressed. Recent studies have found that myocardial energy metabolism was closely related to heart failure, in which substrate utilization, as well as intermediate metabolism disorders, insulin resistance, oxidative stress, and mitochondrial dysfunction, might underlie systolic dysfunction and progression of HF. This article centers on the changes and counteraction of cardiac energy metabolism in the failing heart. Therefore, targeting impaired energy provision is of great potential in the treatment of HF. And shifting the objective from traditional neurohormones to improving the cellular environment is expected to further optimize the management of HF.

An overview of receptor endocytosis and signaling

Endocytosis is a cellular process which mediates receptor internalization, nutrient uptake, and the regulation of cell signaling. Microorganisms (many bacteria and viruses) and toxins also use the same process and enter the cells. Generally, endocytosis is considered in the three forms such as phagocytosis (cell eating), pinocytosis (cell drinking), and highly selective receptor-mediated endocytosis (clathrin-dependent and independent). Several endocytic routes exist in an analogous, achieving diverse functions. Most studies on endocytosis have used transformed cells in culture. To visualize the receptor internalization, trafficking, and signaling in subcellular organelles, a green fluorescent protein-tagged receptor has been utilized. It also helps to visualize the endocytosis effects in live-cell imaging. Confocal laser microscopy increases our understanding of receptor endocytosis and signaling. Site-directed mutagenesis studies demonstrated that many short-sequence motifs of the cytoplasmic domain of receptors significantly play a vital role in receptor internalization, subcellular trafficking, and signaling. However, other factors also regulate receptor internalization through clathrin-coated vesicles. Receptor endocytosis can occur through clathrin-dependent and clathrin-independent pathways. This chapter briefly discusses the internalization, trafficking, and signaling of various receptors in normal conditions. In addition, it also highlights the malfunction of the receptor in disease conditions.

Beta receptor blocker therapy for the elderly in the COVID-19 era

When the coronavirus disease 2019 (COVID-19) pandemic spread globally from the Hubei region of China in December 2019, the impact on elderly people was particularly unfavorable. The mortality associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was highest in older individuals, in whom frailty and comorbidities increased susceptibility to severe forms of COVID-19. Unfortunately, in older patients, the course of COVID-19 was often characterized by significant cardiovascular complications, such as heart failure decompensation, arrhythmias, pericarditis, and myopericarditis. Ensuring that the elderly have adequate therapeutic coverage against known cardiovascular diseases and risk factors is particularly important in the COVID-19 era. Beta blockers are widely used for the treatment and prevention of cardiovascular disease. The clinical benefits of beta blockers have been confirmed in elderly patients, and in addition to their negative chronotropic effect, sympathetic inhibition and anti-inflammatory activity are theoretically of great benefit for the treatment of COVID-19 infection. Beta blockers have not been clearly shown to prevent SARS-CoV-2 infection, but there is evidence from published studies including elderly patients that beta blockers are associated with a more favorable clinical course of COVID-19 and reduced mortality. In this minireview, we summarize the most important evidence available in the literature on the usefulness of beta blocker therapy for older patients in the context of the COVID-19 pandemic.

Perioperative Supplemental Oxygen and Plasma Catecholamine Concentrations after Major Abdominal Surgery-Secondary Analysis of a Randomized Clinical Trial

Perioperative stress is associated with increased sympathetic activity that leads to increases in heart rate and blood pressure, which are associated with the development of perioperative myocardial ischemia. In healthy volunteers, it was shown that the administration of supplemental oxygen attenuated sympathetic nerve activity and subsequently led to lower plasma catecholamine concentrations. We therefore tested the hypothesis that perioperative supplemental oxygen attenuates sympathetic nerve in patients at risk for cardiovascular complications undergoing major abdominal surgery. We randomly assigned 81 patients to receive either 80% or 30% inspired oxygen concentration throughout surgery and the first two postoperative hours. We assessed noradrenaline, adrenaline, and dopamine plasma concentrations before the induction of anesthesia, two hours after surgery and on the third postoperative day. There was no significant difference in postoperative noradrenaline (effect estimated: −41.5 ng·L⁻¹, 95%CI −134.3, 51.2; p = 0.38), adrenaline (effect estimated: 11.2 ng·L⁻¹, 95%CI −7.6, 30.1; p = 0.24), and dopamine (effect estimated: −1.61 ng·L⁻¹, 95%CI −7.2, 3.9; p = 0.57) concentrations between both groups. Based on our results, it seems unlikely that supplemental oxygen influences endogenous catecholamine release in the perioperative setting.

Cell therapy rescues aging-induced beta-1 adrenergic receptor and GRK2 dysfunction in the coronary microcirculation

Our past study showed that coronary arterioles isolated from adipose-derived stromal vascular fraction (SVF)-treated rats showed amelioration of the age-related decrease in vasodilation to beta-adrenergic receptor (β-AR) agonist and improved β-AR-dependent coronary flow and microvascular function in a model of advanced age. We hypothesized that intravenously (i.v.) injected SVF improves coronary microvascular function in aged rats by re-establishing the equilibrium of the negative regulators of the internal adrenergic signaling cascade, G-protein receptor kinase 2 (GRK2) and G-alpha inhibitory (Gαi) proteins, back to youthful levels. Female Fischer-344 rats aged young (3 months, n = 24), old (24 months, n = 26), and old animals that received 1 × 10⁷ green fluorescent protein (GFP+) SVF cells (O + SVF, n = 11) 4 weeks prior to sacrifice were utilized. Overnight urine was collected prior to sacrifice for catecholamine measurements. Cardiac samples were used for western blotting while coronary arterioles were isolated for pressure myography studies, immunofluorescence staining, and RNA sequencing. Coronary microvascular levels of the β1 adrenergic receptor are decreased with advancing age, but this decreased expression was rescued by SVF treatment. Aging led to a decrease in phosphorylated GRK2 in cardiomyocytes vs. young control with restoration of phosphorylation status by SVF. In vessels, there was no change in genetic transcription (RNAseq) or protein expression (immunofluorescence); however, inhibition of GRK2 (paroxetine) led to improved vasodilation to norepinephrine in the old control (OC) and O + SVF, indicating greater GRK2 functional inhibition of β1-AR in aging. SVF works to improve adrenergic-mediated vasodilation by restoring the β1-AR population and mitigating signal cascade inhibitors to improve vasodilation.

Neurohormones, inflammatory mediators, and cardiovascular injury in the setting of heart failure

Neurohormones and inflammatory mediators have effects in both the heart and the peripheral vasculature. In patients with heart failure (HF), neurohormonal activation and increased levels of inflammatory mediators promote ventricular remodeling and development of HF, as well as vascular dysfunction and arterial stiffness. These processes may lead to a vicious cycle, whereby arterial stiffness perpetuates further ventricular remodeling leading to exacerbation of symptoms. Although significant advances have been made in the treatment of HF, currently available treatment strategies slow, but do not halt, this cycle. The current treatment for HF patients involves the inhibition of neurohormonal activation, which can reduce morbidity and mortality related to this condition. Beyond benefits associated with neurohormonal blockade, other strategies have focused on inhibition of inflammatory pathways implicated in the pathogenesis of HF. Unfortunately, attempts to target inflammation have not yet been successful to improve prognosis of HF. Further work is required to interrupt key maladaptive mechanisms involved in disease progression.

Deletion of cardiac polycystin 2/PC2 results in increased SR calcium release and blunted adrenergic reserve

Transient receptor potential proteins (TRPs) act as nonselective cation channels. Of the TRP channels, PC2 (also known as polycystin 2) is localized to the sarcoplasmic reticulum (SR); however, its contribution to calcium-induced calcium release and overall cardiac function in the heart is poorly understood. The goal of this study was to characterize the effect of cardiac-specific PC2 deletion in adult cardiomyocytes and in response to chronic β-adrenergic challenge. We used a temporally inducible model to specifically delete PC2 from cardiomyocytes (Pkd2 KO) and characterized calcium and contractile dynamics in single cells. We found enhanced intracellular calcium release after Pkd2 KO, and near super-resolution microscopy analysis suggested this was due to close localization of PC2 to the ryanodine receptor. At the organ level, speckle-tracking echocardiographical analysis showed increased dyssynchrony in the Pkd2 KO mice. In response to chronic adrenergic stimulus, cardiomyocytes from the Pkd2 KO had no reserve β-adrenergic calcium responses and significantly attenuated wall motion in the whole heart. Biochemically, without adrenergic stimulus, there was an overall increase in PKA phosphorylated targets in the Pkd2 KO mouse, which decreased following chronic adrenergic stimulus. Taken together, our results suggest that cardiac-specific PC2 limits SR calcium release by affecting the PKA phosphorylation status of the ryanodine receptor, and the effects of PC2 loss are exacerbated upon adrenergic challenge.NEW & NOTEWORTHY Our goal was to characterize the role of the transient receptor potential channel polycystin 2 (PC2) in cardiomyocytes following adult-onset deletion. Loss of PC2 resulted in decreased cardiac shortening and cardiac dyssynchrony and diminished adrenergic reserve. These results suggest that cardiac-specific PC2 modulates intracellular calcium signaling and contributes to the maintenance of adrenergic pathways.

TAK733 attenuates adrenergic receptor-mediated cardiomyocyte hypertrophy via inhibiting ErkThr188 phosphorylation

BACKGROUND

Cardiac hypertrophy is an important risk factor for heart failure. The MEK-ERK axis has been reported as a major regulator in controlling cardiac hypertrophy. TAK733 is a potent and selective MEK inhibitor that suppresses cell growth in a broad range of cell lines.

OBJECTIVE

Therefore, we aimed to investigate the anti-hypertrophic effect of TAK733 in cardiomyocytes.

METHODS

Cardiomyocyte hypertrophy was induced with norepinephrine (NE) or phenylepinephrine (PE) using H9c2 cells. To confirm the cardiomyocyte hypertrophy, cell size and protein synthesis were measured and hypertrophy-related gene expression was estimated by reverse transcription polymerase chain reaction. To identify the signaling pathway involved, immunoblot analysis were performed.

RESULTS

We observed that NE activated MEK-ERK signaling and increased ANP and BNP expression, resulting in cardiomyocyte hypertrophy. TAK733 significantly reduced cardiomyocyte hypertrophy by regulating NE-induced ERK1/2 and ERKThr188 activation, hypertrophy marker expression, and cardiomyocyte hypertrophy through depression of MEK activity. In addition, we examined that PE-induced cardiomyocyte hypertrophy was also attenuated by TAK733.

CONCLUSIONS

Here, we report that TAK733 suppressed NE- or PE-induced cardiomyocyte hypertrophy by repressing a crucial component of cardiac hypertrophy-related pathways. These results suggest that TAK733 may be a useful therapeutics for cardiac hypertrophy and warrants further in vivo studies.

Differential effects of long-term slow-pressor and subpressor angiotensin II on contractile and relaxant reactivity of resistance versus conductance arteries

Vascular reactivity was evaluated in three separate arteries isolated from rats after angiotensin II (Ang II) was infused chronically in two separate experiments, one using a 14-day high, slow-pressor dose known to produce hypertension and the other using a 7-day low, subpressor but hypertensive-sensitizing dose. There were three new findings. First, there was no evidence of altered vascular reactivity in resistance arteries that might otherwise explain the hypertension due to the high Ang II or the hypertensive-sensitizing effect of the low Ang II dose. Second, the high Ang II dose exerted a novel differential effect on arterial contractile responsiveness to the sympathetic neurotransmitter, norepinephrine, depending on the level of sympathetic innervation. It clearly enhanced that responsiveness in the sparsely innervated aorta but not in small mesenteric resistance arteries or the proximal (conductance) portion of the caudal artery, both of which are densely innervated. This suggests that the increased expression of alpha adrenergic receptors after long-term exposure to Ang II as previously reported for aortic smooth muscle, is prevented in densely innervated arteries, likely due to long-term Ang II-mediated increase in sympathetic neural traffic to those vessels. Third, the same high dose of Ang II impaired aortic relaxation in response to the nitric oxide (NO) donor nitroprusside without impairing aortic endothelium-dependent relaxation. NO is the main relaxing substance released by aortic endothelium. Accordingly, it is possible that this dose of Ang II is also associated with enhanced release of and/or enhanced smooth muscle responsiveness to other endothelial relaxing substances in a compensatory capacity.

Sirtuin 5 is required for mouse survival in response to cardiac pressure overload

In mitochondria, the sirtuin SIRT5 is an NAD+-dependent protein deacylase that controls several metabolic pathways. Although a wide range of SIRT5 targets have been identified, the overall function of SIRT5 in organismal metabolic homeostasis remains unclear. Given that SIRT5 expression is highest in the heart and that sirtuins are commonly stress-response proteins, we used an established model of pressure overload-induced heart muscle hypertrophy caused by transverse aortic constriction (TAC) to determine SIRT5's role in cardiac stress responses. Remarkably, SIRT5KO mice had reduced survival upon TAC compared with wild-type mice but exhibited no mortality when undergoing a sham control operation. The increased mortality with TAC was associated with increased pathological hypertrophy and with key abnormalities in both cardiac performance and ventricular compliance. By combining high-resolution MS-based metabolomic and proteomic analyses of cardiac tissues from wild-type and SIRT5KO mice, we found several biochemical abnormalities exacerbated in the SIRT5KO mice, including apparent decreases in fatty acid oxidation and glucose oxidation as well as an overall decrease in mitochondrial NAD+/NADH. Together, these abnormalities suggest that SIRT5 deacylates protein substrates involved in cellular oxidative metabolism to maintain mitochondrial energy production. Overall, the functional and metabolic results presented here suggest an accelerated development of cardiac dysfunction in SIRT5KO mice in response to TAC, explaining increased mortality upon cardiac stress. Our findings reveal a key role for SIRT5 in maintaining cardiac oxidative metabolism under pressure overload to ensure survival.

Sympathetic Activation in Chronic Heart Failure: Potential Benefits of Interventional Therapies

Heart failure (HF) is a major and growing public health problem. This condition is associated with poor prognosis, a high rate of mortality, frequent hospitalization and increasing costs to health care systems. Pharmacological approaches aimed at reducing morbidity and mortality in HF have primarily focused on inhibition of the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system (SNS), both of which have been associated with disease development, progression and adverse cardiovascular (CV) outcomes. The increasing number of hospitalizations for HF decompensation suggests the failure of available treatment options, indicating the necessity for alternative therapeutic approaches. Alongside pharmacological and cardiac resynchronization therapies in selected patients with arrhythmia, recent advancements in the management of HF have been directed at inhibiting relevant neurogenic pathways underlying disease development and progression. Initial evidence regarding the safety and effectiveness of interventional procedures suggests that HF patients may benefit from novel adjunctive therapies. Here we review the critical role of sympathetic activation in HF and the rationale for therapeutic interventions including device-based and interventional approaches aimed at restoring autonomic neural balance in this condition.

Effect of adenovirus mediated β2-AR overexpression on IL-10 level secreted by cardiomyocytes of heart failure rats

The effect of β₂-adrenergic receptor (AR) overexpression on interleukin (IL)-10 content secreted by cardiomyocytes of heart failure (HF) rats was investigated. A rat model of chronic HF was established by partially banding abdominal aorta and the cardiomyocytes were isolated with collagenase II. The cardiomyocytes were then transfected with adenovirus type 5-ADRβ₂-enhanced green fluorescent protein (EGFP) for 48 h to observe the changes of β₂-AR protein expression using western blot analysis. The IL-10 level was detected by ELISA. The experiment was divided into seven groups: Control, HF, HF+EGFP, HF+β₂, sham, sham+EGFP and sham+β₂ groups. Compared with the sham-operated group, left ventricular diastolic dimension, and left ventricular systolic dimension were increased (P<0.05), whereas ejection fraction and fractional shortening were decreased (P<0.05) in the HF group. Compared with the sham group, the cardiomyocyte survival rate of the HF group was significantly reduced (P<0.05). Compared with the control or sham group, the β₂-AR protein level of the HF group showed no significant differences (P>0.05). Compared with the HF and HF+EGFP groups, the expression of β₂-AR protein of cardiomyocytes was increased in the HF+β₂ group (P<0.05). Compared with the sham group, IL-10 content secreted by cardiomyocytes in the HF group was increased (P<0.05). Compared with the HF and HF+EGFP groups, IL-10 content in the HF+β₂ group was increased significantly (P<0.05). In conclusion, the concentration of IL-10 secreted by cardiomyocytes of HF rats was increased. The overexpression of β₂-AR in the cardiomyocytes of HF rats was able to enhance the secretion of IL-10.

Cardiac Dysfunction Induced by Obesity Is Not Related to β-Adrenergic System Impairment at the Receptor-Signalling Pathway

Obesity has been shown to impair myocardial performance. Some factors have been suggested as responsible for possible cardiac abnormalities in models of obesity, among them beta-adrenergic (βA) system, an important mechanism of regulation of myocardial contraction and relaxation. The objective of present study was to evaluate the involvement of βA system components in myocardial dysfunction induced by obesity. Thirty-day-old male Wistar rats were distributed in control (C, n = 25) and obese (Ob, n = 25) groups. The C group was fed a standard diet and Ob group was fed four unsaturated high-fat diets for 15 weeks. Cardiac function was evaluated by isolated papillary muscle preparation and βA system evaluated by using cumulative concentrations of isoproterenol and Western blot. After 15 weeks, the Ob rats developed higher adiposity index than C rats and several comorbidities; however, were not associated with changes in systolic blood pressure. Obesity caused structural changes and the myocardial responsiveness to post-rest contraction stimulus and increased extracellular calcium (Ca²⁺) was compromised. There were no changes in cardiac function between groups after βA stimulation. The obesity was not accompanied by changes in protein expression of G protein subunit alpha (Gsα) and βA receptors (β₁AR and β₂AR). In conclusion, the myocardial dysfunction caused by unsaturated high-fat diet-induced obesity, after 15 weeks, is not related to βAR system impairment at the receptor-signalling pathway.

An analytic tool for prediction of hemodynamic responses to vasopressors

This paper presents a new analytic tool for automated control of vasopressor infusion, which uses measured changes in blood pressure to infer changes in the underlying cardiovascular system and then estimate dose-response relationships for the underlying cardinal cardiovascular parameters, i.e., those related to cardiac output (CO) and total peripheral resistance (TPR). Ultimately, blood pressure as a function of vasopressor dose is predicted based on the estimated underlying cardiovascular state by extrapolating the dose-response relationship. As well, this tool adapts to individual subjects with a minimum of individualized training data. In this report, proof-of-principle is provided using experimental epinephrine dose-response data from four different sets of subjects. Given two observations from different infusion rates, the analytic tool was able to accurately predict the groups' blood pressure, heart rate, TPR, stroke volume, and CO as a function of vasopressor dose levels: the root-mean-squared prediction error for the mean arterial pressure (MAP) was consistently smaller than 5% of the underlying MAP; the r(2) values for the TPR, stroke volume, and CO were consistently higher than 0.96; and the limits of agreement between actual versus predicted blood pressure (BP), TPR, stroke volume, and CO were consistently smaller than 8% of the respective underlying values. The proposed analytic tool may provide a meaningful step towards automated control of vasopressor therapy.

Blockade of β-adrenoceptors restores the GRK2-mediated adrenal α(2) -adrenoceptor-catecholamine production axis in heart failure

BACKGROUND AND PURPOSE

Sympathetic nervous system (SNS) hyperactivity is characteristic of chronic heart failure (HF) and significantly worsens prognosis. The success of β-adrenoceptor antagonist (β-blockers) therapy in HF is primarily attributed to protection of the heart from the noxious effects of augmented catecholamine levels. β-Blockers have been shown to reduce SNS hyperactivity in HF, but the underlying molecular mechanisms are not understood. The GPCR kinase-2 (GRK2)-α(2) adrenoceptor-catecholamine production axis is up-regulated in the adrenal medulla during HF causing α(2) -adrenoceptor dysfunction and elevated catecholamine levels. Here, we sought to investigate if β-blocker treatment in HF could lower SNS activation by directly altering adrenal GRK2 levels.

EXPERIMENTAL APPROACH

Four weeks after myocardial infarction-induced HF, adult rats were randomized to 10-week treatment with vehicle (HF/C) or bisoprolol (HF/B). Cardiac function and dimensions were measured. In heart and adrenal gland, GRK2 levels were assessed by RT-PCR and Western blotting and adrenoceptors studied with radioligand binding. Catecholamines and α(2) adrenoceptors in adrenal medulla chromaffin cell cultures were also measured.

KEY RESULTS

Bisoprolol treatment ameliorated HF-related adverse cardiac remodelling and reduced plasma catecholamine levels, compared with HF/C rats. Bisoprolol also attenuated adrenal GRK2 overexpression as observed in HF/C rats and increased α(2) adrenoceptor density. In cultures of adrenal medulla chromaffin cells from all study groups, bisoprolol reversed HF-related α(2) adrenoceptor dysfunction. This effect was reversed by GRK2 overexpression.

CONCLUSION AND IMPLICATIONS

Blockade of β-adrenoceptors normalized the adrenal α(2) adrenoceptor-catecholamine production axis by reducing GRK2 levels. This effect may contribute significantly to the decrease of HF-related sympathetic overdrive by β-blockers.

hERG K+ Channels: Structure, Function, and Clinical Significance

The human ether-a-go-go related gene (hERG) encodes the pore-forming subunit of the rapid component of the delayed rectifier K+ channel, Kv11.1, which are expressed in the heart, various brain regions, smooth muscle cells, endocrine cells, and a wide range of tumor cell lines. However, it is the role that Kv11.1 channels play in the heart that has been best characterized, for two main reasons. First, it is the gene product involved in chromosome 7-associated long QT syndrome (LQTS), an inherited disorder associated with a markedly increased risk of ventricular arrhythmias and sudden cardiac death. Second, blockade of Kv11.1, by a wide range of prescription medications, causes drug-induced QT prolongation with an increase in risk of sudden cardiac arrest. In the first part of this review, the properties of Kv11.1 channels, including biogenesis, trafficking, gating, and pharmacology are discussed, while the second part focuses on the pathophysiology of Kv11.1 channels.

IL-33 independently induces eosinophilic pericarditis and cardiac dilation: ST2 improves cardiac function

BACKGROUND

IL-33 through its receptor ST2 protects the heart from myocardial infarct and hypertrophy in animal models but, paradoxically, increases autoimmune disease. In this study, we examined the effect of IL-33 or ST2 administration on autoimmune heart disease.

METHODS AND RESULTS

We used pressure-volume relationships and isoproterenol challenge to assess the effect of recombinant (r) IL-33 or rST2 (eg, soluble ST2) administration on the development of autoimmune coxsackievirus B3 myocarditis and dilated cardiomyopathy in male BALB/c mice. The rIL-33 treatment significantly increased acute perimyocarditis (P=0.006) and eosinophilia (P=1.3×10(-5)), impaired cardiac function (maximum ventricular power, P=0.0002), and increased ventricular dilation (end-diastolic volume, P=0.01). The rST2 treatment prevented eosinophilia and improved heart function compared with rIL-33 treatment (ejection fraction, P=0.009). Neither treatment altered viral replication. The rIL-33 treatment increased IL-4, IL-33, IL-1β, and IL-6 levels in the heart during acute myocarditis. To determine whether IL-33 altered cardiac function on its own, we administered rIL-33 to undiseased mice and found that rIL-33 induced eosinophilic pericarditis and adversely affected heart function. We used cytokine knockout mice to determine that this effect was due to IL-33-mediated signaling but not to IL-1β or IL-6.

CONCLUSIONS

We show for the first time to our knowledge that IL-33 induces eosinophilic pericarditis, whereas soluble ST2 prevents eosinophilia and improves systolic function, and that IL-33 independently adversely affects heart function through the IL-33 receptor.

Merits of non-invasive rat models of left ventricular heart failure

Heart failure (HF) is characterized as a limitation to cardiac output that prevents the heart from supplying tissues with adequate oxygen and predisposes individuals to pulmonary edema. Impaired cardiac function is secondary to either decreased contractility reducing ejection (systolic failure), diminished ventricular compliance preventing filling (diastolic failure), or both. To study HF etiology, many different techniques have been developed to elicit this condition in experimental animals, with varying degrees of success. Among rats, surgically induced HF models are the most prevalent, but they bear several shortcomings, including high mortality rates and limited recapitulation of the pathophysiology, etiology, and progression of human HF. Alternatively, a number of non-invasive HF induction methods avoid many of these pitfalls, and their merits in technical simplicity, reliability, survivability, and comparability to the pathophysiologic and pathogenic characteristics of HF are reviewed herein. In particular, this review focuses on the primary pathogenic mechanisms common to genetic strains (spontaneously hypertensive and spontaneously hypertensive heart failure), pharmacological models of toxic cardiomyopathy (doxorubicin and isoproterenol), and dietary salt models, all of which have been shown to induce left ventricular HF in the rat. Additional non-invasive techniques that may potentially enable the development of new HF models are also discussed.

Lipolytic effects of B-type natriuretic peptide 1-32 in adipose tissue of heart failure patients compared with healthy controls

OBJECTIVES

Our goal was to examine the role of B-type natriuretic peptide (BNP) in lipolysis regulation in heart failure (HF) patients.

BACKGROUND

Enhanced adipose tissue lipolysis can contribute to myocardial lipid overload, insulin resistance, and cachexia in advanced HF. Natriuretic peptides were recently recognized to stimulate lipolysis in healthy subjects.

METHODS

Ten nondiabetic HF patients (New York Heart Association functional class III, 50% nonischemic etiology) and 13 healthy subjects (control subjects) of similar age, sex, and body composition underwent a microdialysis study of subcutaneous abdominal adipose tissue. Four microdialysis probes were simultaneously perfused with 0.1 μM BNP(1-32,) 10 μM BNP(1-32), 10 μM norepinephrine (NE) or Ringer's solution. Outgoing dialysate glycerol concentration (DGC) was measured as an index of lipolysis.

RESULTS

Spontaneous lipolysis was higher in HF patients compared with control subjects (DGC: 189 ± 37 μmol/l vs. 152 ± 35 μmol/l, p < 0.01). Response to NE was similar (p = 0.35) in HF patients and control subjects (DGC increase of 1.7 ± 0.2-fold vs. 1.7 ± 0.4-fold). BNP(1-32) 10 μM markedly increased lipolysis in both HF patients and control subjects (DGC increase of 2.8 ± 0.5-fold vs. 3.2 ± 0.3-fold), whereas the response to 0.1 μM BNP(1-32) was more pronounced in HF patients (p = 0.02). In HF patients, spontaneous lipolysis positively correlated with insulin resistance and the response to BNP(1-32) negatively correlated with adiposity.

CONCLUSIONS

BNP(1-32) exerts strong lipolytic effects in humans. Despite marked elevation of plasma immunoreactive BNP, the responsiveness of adipose tissue to BNP(1-32) is not attenuated in HF, possibly reflecting a deficiency of endogenous bioactive BNP. Lipolytic effects of BNP can contribute to excessive fatty acid mobilization in advanced HF.

Cardiac function following prolonged exercise: influence of age

This study sought to determine the influence of age on the left ventricular (LV) response to prolonged exercise (PE; 150 min). LV systolic and diastolic performance was assessed using echocardiography (ECHO) before (pre) and 60 min following (post) exercise performed at 80% maximal aerobic power in young (28 ± 4.5 years; n = 18; mean ± SD) and middle-aged (52 ± 3.9 years; n = 18) participants. LV performance was assessed using two-dimensional ECHO, including speckle-tracking imaging, to determine LV strain (LV S) and LV S rate (LV SR), in addition to Doppler measures of diastolic function. We observed a postexercise elevation in LV S (young: −19.5 ± 2.1% vs. −21.6 ± 2.1%; middle-aged: −19.9 ± 2.3% vs. −20.8 ± 2.1%; P < 0.05) and LV SR (young: −1.19 ± 0.1 vs. −1.37 ± 0.2; middle-aged: −1.20 ± 0.2 vs. −1.38 ± 0.2; P < 0.05) during recovery in both groups. Diastolic function was reduced during recovery, including the LV SR ratio of early-to-late atrial diastolic filling (SRe/a), in young (2.35 ± 0.7 vs. 1.89 ± 0.5; P < 0.01) and middle-aged (1.51 ± 0.5 vs. 1.05 ± 0.2; P < 0.01) participants, as were conventional indices including the E/A ratio. Dobutamine stress ECHO revealed a postexercise depression in LV S in response to increasing dobutamine dose, which was similar in both young (pre-exercise dobutamine 0 vs. 20 μg·kg−1·min−1: −19.5 ± 2.1 vs. −27.2 ± 2.2%; postexercise dobutamine 0 vs. 20 μg·kg−1·min−1: −21.6 ± 2.1 vs. −23.7 ± 2.2%; P < 0.05) and middle-aged participants (pre: −19.9 ± 2.3 vs. −25.3 ± 2.7%; post: −20.8 ± 2.1 vs. −23.5 ± 2.7; P < 0.05). This was despite higher noradrenaline concentrations immediately postexercise in the middle-aged participants compared with young (4.26 ± 2.7 nmol/L vs. 3.00 ± 1.4 nmol/L; P = 0.12). These data indicate that LV dysfunction is observed following PE and that advancing age does not increase the magnitude of this response.

Urocortin-2 induces vasorelaxation of coronary arteries isolated from patients with heart failure

1. Urocortin-2 (Ucn2) is a vasoactive peptide belonging to the corticotrophin-releasing factor (CRF) family that has potent cardiovascular actions. It has been suggested that Ucn2 participates in the pathophysiology of heart failure. However, little is known about the mechanisms underlying the action of Ucn2 in human coronary arteries. The aim of the present study was to assess the effects of Ucn2 on the vascular tone of human coronary arteries dissected from heart failure patients. 2. Human coronary arteries were dissected from the hearts of patients subjected to orthotopic heart transplantation. Coronary arteries were obtained from 17 patients with heart failure due to dilated cardiomyopathy of ischaemic origin in Stage III-IV of the New York Heart Association classification. Changes in tone were measured in arterial rings using force transducers. 3. Application of increasing concentrations of Ucn2 (5-20 nmol/L) to arterial rings precontracted with agonists induced dose-dependent relaxation of the coronary artery, which was independent of endothelial cell activation. Furthermore, the inhibition of the adenylyl cyclase by MDL-12 (100 nmol/L) and protein kinase A (PKA) by H89 (1 μmol/L) prevented Ucn2-mediated relaxation of coronary artery rings. 4. The results of the present study suggest that, in heart failure patients, Ucn2 could be useful in modulating coronary artery circulation independent of endothelial integrity through mechanisms that involve adenylyl cyclase activation and PKA stimulation. The findings warrant further investigation of the role of Ucn2 in circulatory regulation and its potential therapeutic application in heart disease.

Role of the excessive amounts of circulating catecholamines and glucocorticoids in stress-induced heart disease

Various stressful stimuli are known to activate the sympathetic nervous system to release catecholamines and the hypothalamic-pituitary-adrenal axis to release glucocorticoids in the circulation. Although initial actions of both catecholamines and glucocorticoids are beneficial for the function of the cardiovascular system, their delayed effects on the heart are deleterious. Glucocorticoids not only increase plasma levels of catecholamines by inhibiting their extraneuronal uptake, but they have also been shown to induce supersensitivity to catecholamines in the heart by upregulating different components of the betta-adrenoceptor signal transduction system. Low concentrations of catecholamines stimulate the heart by promoting Ca2+ movements, whereas excessive amounts of catecholamines produce cardiac dysfunction by inducing intracellular Ca2+ overload in cardiomyocytes. Several studies have shown, however, that under stressful conditions high concentrations of catecholamines become oxidized to form aminolutins and generate oxyradicals. These oxidation products of catecholamines have been demonstrated to produce coronary spasm, arrhythmias, and cardiac dysfunction by inducing Ca2+-handling abnormalities in both sarcolemmal and sarcoplasmic reticulum, defects in energy production by mitochondria, and myocardial cell damage. In this article we have focused the discussion to highlight the interrelationship between catecholamines and glucocorticoids and to emphasize the role of oxidation products of catecholamines in the development of stress-induced heart disease.

Catecholamine-induced myocardial fibrosis and oxidative stress is attenuated by Terminalia arjuna (Roxb.)

Objectives

Myocardial fibrosis and oxidative stress accompany a number of cardiac disorders such as hypertrophic cardiomyopathy, hypertensive heart disease and cardiac failure. Stem bark of Terminalia arjuna has been advocated for cardiac ailments. The present study evaluated the effects of T. arjuna bark extract on myocardial fibrosis and oxidative stress induced by chronic beta-adrenoceptor stimulation.

Methods

Aqueous extract of T. arjuna bark was evaluated at 63, 125 and 250 mg/kg given orally for antifibrotic and antioxidant effects in rats given the selective β-adrenoceptor agonist isoprenaline (5 mg/kg s.c.) for 28 days. Captopril (50 mg/kg per day, given orally), an inhibitor of angiotensin-converting enzyme used as a standard cardioprotective drug, was used as a positive control.

Key findings

Isoprenaline caused fibrosis, increased oxidative stress and cardiac hypertrophy (increased heart weight: body weight ratio and cardiomyocyte diameter). The T. arjuna bark extract and captopril significantly prevented the isoprenaline-induced increase in oxidative stress and decline in endogenous antioxidant level. Both also prevented fibrosis but not the increase in heart weight: body weight ratio.

Conclusions

T. arjuna protects against myocardial changes induced by chronic beta-adrenoceptor stimulation.

The role of N-terminal pro-brain natriuretic peptide (NT-pro-BNP) as a prognostic marker in older people: the impact of reduced renal function

The N-terminal pro-brain natriuretic peptide (NT-pro-BNP) is released in response to volume expansion and/or increased tension on left ventricular myocytes. NT-pro-BNP is a useful diagnostic and prognostic biomarker both in patients with dyspnoea of unknown aetiology, and for risk assessment of patients with established heart failure. However, impaired kidney function – a common condition in older people as well as a strong risk factor for cardiovascular disease is associated with elevated circulating levels of NT-pro-BNP. Therefore, it is important to know the kidney function when interpreting an elevated NT-pro-BNP measurement obtained in older people in order to diagnose or stage congestive heart failure.

Activation of Gi induces mechanical hyperalgesia poststress or inflammation

In studies of the role of primary afferent nociceptor plasticity in the transition from acute to chronic pain we recently reported that exposure to unpredictable sound stress or a prior inflammatory response induces long-term changes in the second messenger signaling pathway, in nociceptors, mediating inflammatory hyperalgesia; this change involves a switch from a G(s)-cAMP-PKA to a G(i)-PKCepsilon signaling pathway. To more directly study the role of G(i) in mechanical hyperalgesia we evaluated the nociceptive effect of the G(i) activator, mastoparan. Intradermal injection of mastoparan in the rat hind paw induces dose-dependent (0.1 ng-1 microg) mechanical hyperalgesia. The highly selective inhibitors of G(i), pertussis toxin, and of protein kinase C epsilon (PKCepsilon), PKCepsilonV(1-2), both markedly attenuate mastoparan-induced hyperalgesia in stressed rats but had no effect on mastoparan-induced hyperalgesia in unstressed rats. Similar effects were observed, at the site of nociceptive testing, after recovery from carrageenan-induced inflammation. These studies provide further confirmation for a switch to a G(i)-activated and PKCepsilon-dependent signaling pathway in primary mechanical hyperalgesia, induced by stress or inflammation.

Stress induces a switch of intracellular signaling in sensory neurons in a model of generalized pain

Stress dramatically exacerbates pain in diseases such as fibromyalgia and rheumatoid arthritis, but the underlying mechanisms are unknown. We tested the hypothesis that stress causes generalized hyperalgesia by enhancing pronociceptive effects of immune mediators. Rats exposed to nonhabituating sound stress exhibited no change in mechanical nociceptive threshold, but showed a marked increase in hyperalgesia evoked by local injections of prostaglandin E(2) or epinephrine. This enhancement, which developed more than a week after exposure to stress, required concerted action of glucocorticoids and catecholamines at receptors located in the periphery on sensory afferents. The altered response to pronociceptive mediators involved a switch in coupling of their receptors from predominantly stimulatory to inhibitory G-proteins (G(s) to G(i)), and for prostaglandin E(2), emergence of novel dependence on protein kinase C epsilon. Thus, an important mechanism in generalized pain syndromes may be stress-induced coactivation of the hypothalamo-pituitary-adrenal and sympathoadrenal axes, causing a long-lasting alteration in intracellular signaling pathways, enabling normally innocuous levels of immune mediators to produce chronic hyperalgesia.